This invention relates to continuous mining machines that employ rotary boring heads.
There are commonly used in the mining industry, continuous mining machines of the boring type which include a mobile frame and a plurality of boring heads mounted thereon. These heads are rotatable about parallel axes and cut a plurality of contiguous bores at the front of the machine. Typically, there are two boring heads or rotors which rotate in opposite directions in such a way as not to interfere with each other but machines with more than two rotors are also known. The machine is usually driven with caterpillar like tracks. In one known machine, the mobile frame is provided with both front tilt cylinders and rear tilt cylinders with both sets of cylinders connected at one end to an upper frame which houses the main gear box, main electric motors and the rotating boring heads. With the use of these cylinders, it is possible to change the direction of the cutting heads, moving them either upwardly or downwardly. The mined material that is cut by the boring heads is conveyed up the centre of the machine with a drag type conveyor. The two rotors are able to cut this material by means of cutting bits mounted on the front of the rotor arms.
One difficulty with this type of boring machine is that the rotating heads leave both downwardly extending and upstanding cusps that are between the boring heads as the machine is advanced. Some method must be provided to trim or cut off these cusps. In one well known continuous mining machine, there is mounted behind the two rotors and in front of the gear box two steel bars, one at the top of the rotating heads and the other at the bottom. On these bars are mounted steel glides along which a trim chain runs. Cutting bits are mounted on this trim chain so as to face the front and cut off the cusps, leaving flat areas at the top and bottom of the bore. The aforementioned bars can be retracted with cylinders which are mounted to the main gear box. The trim chain is driven by a sprocket which is driven from the main gear box.
Problems have been encountered in the past with the aforementioned trim chains because they have high maintenance costs. Although a trim chain typically cuts less than 10% of the face, the trim chain maintenance costs could be as much as 45% of the total cost of maintaining the boring machine. An annual trim chain maintenance on a single boring machine may amount to $80,000.00 Cdn. and these costs do not include lost production and indirect costs.
Also each trim chain in a mining machine is known to require approximately 200 horse power in order to run the chain along its continuous path which includes sprockets and rigid guides. Thus, a tremendous amount of power is required to operate both bottom and top chains while advancing the bore through the ore at even the relatively slow rate of 12" per minute.
It will be appreciated that it is highly desirable to reduce the mechanical breakdown time of a mine boring machine as much as possible. Each time a borer breaks down, all production from the area of operation of the machine stops and a delay from a breakdown can easily last from one to four hours. Because of the frequency of the breakdowns, there is a great amount of frustration on the part of the operators and supervisors, which frustration can lead to low moral.
U.S. Pat. No. 3,086,761 issued Apr. 23, 1963 to Goodman Manufacturing Co., describes a boring type continuous miner with two rotating boring heads, each having three rotating arms. The arms have radially spaced cutter supports projecting forwardly therefrom and carrying the usual cutter bits. This machine has a conveyor extending therealong from a position adjacent the ground rearwardly of a support for a lower trimmer bar. There is also an upper trimmer bar extending between the boring heads and forming a guide for a trimmer cutter chain. The upper bar is mounted on a frame for vertical adjustment by means of hydraulic jacks. The lower trimmer bar is also adjustably mounted on the frame by means of laterally spaced fluid pressure jacks. The cutter chain is guided for movement along the upper and lower trimmer bars and it is trained about corner sprockets at opposite ends of the upper bar. There are also corner sprockets at opposite ends of the lower trimmer bar.
In another version of a boring type mining machine disclosed in U.S. Pat. No. 2,823,023, which issued Feb. 11, 1958 to Goodman Manufacturing Company, there is an auxiliary frame mounted by suitable jacks at the front end of a main frame. There are a pair of boring heads which project forwardly from the auxiliary frame and which rotate on laterally spaced axes. In order to cut the bottom cusp formed by the boring heads, there is a lower trimmer bar which is rotatable on a horizontal axis and journaled near opposite ends thereof. This trimmer bar is located in front of the auxiliary frame and rearwardly of the path of movement of the two boring heads. An upper cutter bar is mounted in a similar manner at the upper limits of movement of the boring heads. Cutter bits are mounted on the spiral ribs formed on the two cutter bars.
It is an object of the present invention to provide an improved continuous mining machine with two rotary boring heads having a plurality of radially extending rotor arms with each rotor arm having mounted therein a pair of reciprocating pole devices which are connected together by means of a link member on which cutter bits are mounted. A cam mechanism is provided to reciprocate the pole devices as the boring heads are rotated. This mechanism causes each pair of pole devices to be pushed radially outwardly at each of four corners distributed about a circular hole cut by the respective boring head in such a manner that the resulting hole bored by the machine is generally rectangular.
It is a further object of the invention to provide a continous mining machine that avoids the need for trim chains and having reduced maintenance costs. Because of the decrease in the downtime for maintenance, the production capability of the machine is increased.